Many older adults have significant visual impairments in spatial contrast sensitivity, acuity, and visual sensitivity, even when they are believed to be in good eye health. Since these impairments cannot be attributed to the presence of ocular or neurological disease, they are believed to reflect the biological aging of the visual system. Visual deficits in the elderly can severely hamper their performance of routine daily activities. With the increase in the older adult population in our society, there is a pressing need to better understand the visual functional problems of the elderly, and to ultimately identify ways in which the quality of visual performance can be maintained despite advancing age. Toward this eventual goal, we will use two different approaches to examine factors which underlie loss of spatial vision in older adults. In Part 1 of this Research Plan we will use psychophysical (behavioral) techniques to examine why spatial contrast sensitivity deficits in the elderly are greatly accentuated at lower light levels. Experiments using laser interferometric techniques will address the contribution of neural vs. optical factors to their sensitivity loss. Additional experiments will examine the roles of spatial summation, internal neural noise, and stimulus uncertainty in producing the exacerbated loss at lower luminance. Older adults' performance in these studies will be compared to that of young adults in good eye health. In Part 2 we will make use of a unique opportunity to measure visual function and retinal topography on the same eyes from a relatively large sample of adults of various ages. These individuals are candidates for orbital exenterations (i.e., eye removal) because of craniofacial cancer. Prior to eye removal, psychophysical studies of spatial resolution and visual sensitivity at various eccentricities will be performed on each patient. Following surgery, retinal topography studies will be carried out which will provide estimates of photoreceptor and ganglion cell densities. Earlier studies attempting to link visual function and retinal topography were based on cross-species or cross-individual comparisons, using very small samples. Our approach, which will be within-species and within-individual, and which will use human subjects, has clear advantages over the previous approach, and will have immediate relevance for understanding visual processing in humans throughout adulthood. Information provided by Parts 1 and 2 of this Research Plan will assist in identifying the mechanisms underlying older adults' loss in spatial vision, which is a crucial first step toward developing interventions to minimize the visual functional problems the elderly face in everyday life.